Presently all blast shelter doors open outwardly, i.e. in the direction of the source of the pressure. This is readily apparent from the abundant commercial literature available. These prior art doors are more easily engineered due to the fact that the external pressure on the door leaf is uniformly distributed over the periphery thereof and accordingly transmitted uniformly to the door frame mounted in a wall of the shelter.
Concern has been raised with respect to prior art blast shelter doors which open outwardly in view of the fact that rubble, debris, soil, etc. can be projected by the force of the explosion against the door and pile up, thereby blocking the door by their own weight and preventing the shelter occupants from opening it. The occupants become entombed inside in the absence of an available emergency exit.
The following prior art U.S. patents, though not exhaustive of the combination door and door frame art, disclose combination doors and door frames of the type described above wherein they open outwardly in the direction of the source of the pressure, i.e. against the overpressure:
U.S. Pat. No. 603,948--Hanlon PA1 U.S. Pat. No. 3,032,835--Saar PA1 U.S. Pat. No. 3,093,098--Rosenfeld PA1 U.S. Pat. No. 3,159,118--Rosenfeld PA1 U.S. Pat. No. 3,585,757--Ritchle et al